Field of the Invention
The invention is generally related to the area of optical communications. In particular, the invention is related to fiber optical switch assembly, and techniques for packaging such an optical switch.
The Background of Related Art
Optical switches are critical building blocks in fiber optical communication networks and other applications. In optical telecommunication, an optical switch is a switch that enables signals in optical fibers to be selectively switched from one end to another. Electromechanical optical switch is one of the commonly used types. It is operated by moving either the ends of input fibers relative to the ends of output fibers, or a mirror/prism to redirect optical signals to a selected output fiber without moving the optical fibers themselves.
Moving a prism is one technique to build a fiber optic switch. As shown in FIG. 1, a prism 102 is employed to switch a light beam, namely an optical signal can enter and leave such a prism with minimum sensitivity from the motion change of the prism. This technique compares favorably against other mirror-based approaches that may double the sensitivity. However a much longer optical pathway 104 in free space is required for the prism directing optical signals than that of moving the fiber ends. The long optical path in the prism motion-based switch makes it sensitive to fiber collimators which have to be fixed precisely and with minimal drift during any environmental changes throughout its service life. Thus, care must be exercised for the collimator fixations in a fiber optic switch and this fixation is critical for high stability and reliability over a large working temperature range and other environment conditions, therefore the packaging of these collimators is of the most important process in manufacturing a fiber optical switch.
In most compact 1×2 and 2×2 fiber optic switch designs, the collimators are packaged by soldering processes to a metal substrate or a metal case. FIG. 2 duplicates FIG. 2 of U.S. Pat. No. 5,867,617. Although the design is simple, the case must be pre-coated with gold, soldering processes is very critical to ensure the reliability of the switching function. One good feature of soldering-based packaging is that if there is any minor position drift of the collimator from the soldering process, resulting in a light loss increase, one can bend the collimator back to readjust its positions because the solder allows certain degree of deformation. One can also meld the solder again if such bend is too hard to do in room temperature. This flexibility to rework can assure a higher manufacturing yield for assembling the switch. This is why in the compact switch (e.g., 1×2 and 2×2) markets, most switches today are being made by soldering processes. In recent years, environmental protection movements have triggered more and more “Green” manufacturing practices, many countries and regions legislated and regulated the use of lead and thus soldering becomes increasingly under pressure.
Although there are lead-free solders available now, higher melting temperature to use them can cause the fixation process more stressful, leading to reliability issues. Also many optical components being soldered may not withstand the high temperature that can weaken the reliability of the components. This prompts the industry to rethink if there are alternative approaches to make optical switches.